This invention is concerned with crank shafts, particularly, but not necessarily exclusively, it is concerned with crank shafts for internal combustion engines. A typical crank shaft for an internal combustion engine of an automobile comprises a unitary or integral structure comprising shaft sections at each end of the crank shaft and a center shaft section, those shaft sections being aligned and being supported in the main bearings of the crank case of the engine. The end shaft sections are secured to counterweights, the center-shaft section is formed between two adjacent counterweights and crank pins are formed between adjacent pairs of counterweights, the crank pins having the connecting rods of the pistons mounted upon them when assembled in an engine.
Major problems of the known integral crank shafts are, of course, the fact that if any one of the crank pins or shaft sections become worn, then the whole of the shaft must be replaced. Additionally, of course, there can be no adjustment for stroke with the conventional crank shaft and any adjustment must be effected by replacing the whole crank shaft with a new crank shaft of a different throw.